As a lens processing method by means of lathing, for example, a processing method disclosed in Japanese Patent Laid-Open No. 11-300501 is known. According to this processing method, a cutting tool employs different cutting edges in accordance with the processing order or the processing portion of the work, so that various types of cutting operations are realized by one cutting tool.
In lens processing by means of the lathe, as shown in FIGS. 20 and 21, a three-dimensional shape is formed on a lens 21 held and rotated by a rotating shaft (spindle) 12 of a lathe 1 by cutting or grinding with a processing tool from a direction perpendicular to the axis of the rotating shaft 12 while a processing locus t concentric or spiral about the rotating shaft 12 as the center is formed.
The lens 21 forms a disc having a thickness in the Z-axis direction which is the axial direction of the rotating shaft of the lathe 1 and spreading to form a surface in two, X- and Y-axis directions perpendicular to the Z-axis. The lens 21 is held such that its X-Y surface coincides with the end face of the rotating shaft 12. At this time, the lens 21 is positioned such that its center (Zo) is concentric with the rotating shaft 12.
The lens 21 is lathed using the processing tool which is sequentially fed in the X- and/or Y-axis and controlled in the Z-axis. The processing tool is formed using one or a plurality of cutting tools each having a constant radius of curvature, and cuts the lens from the direction perpendicular to the axis of the rotating shaft 12 and the axial direction of the rotating shaft 12.
During lathing, the processing position by the processing tool is sequentially fed from the periphery toward the center of the lens 21. The processing position in the Z-axis direction is numerically controlled in accordance with the moving position, so that a predetermined optical surface is formed by cutting or grinding.
The lens 21 is lathed from its outer periphery toward its center. Namely, the processing locus t starts at the periphery of the lens 21 and ends at the center (Zo). This process (path) is repeated a necessary number of times, thus forming a predetermined lens surface.
Lens processing using the lathe can form many different types of shapes by numerically controlling the processing position. Hence, this processing is suitable for processing an aspheric lens such as a progressive-power lens.